1. Field of the Invention
The present invention relates to drive units, methods of producing the same, running body moving units, image reading apparatuses, and imaging apparatuses, and more particularly to a drive unit moving a movable body by a drive wire driven by a drive pulley attached to a drive shaft, a method of producing such a drive unit, a running body moving unit that linearly moves a running body by a driving force transmitted through wires and is applicable to image reading apparatuses such as copiers, facsimile machines, and scanners for reading and scanning an image, an image reading apparatus employing such a running body moving unit, and an imaging apparatus employing such an image reading apparatus.
2. Description of the Related Art
In conventional well-known drive units, movable bodies, which are connected to parts of a drive wire wound around a drive pulley attached to a drive shaft, are moved by the drive wire when the drive shaft is rotated along with the drive pulley.
Such drive units are employed in copiers, facsimile machines, and scanners for moving a read optical system reading an original image.
In conventional reading apparatuses such as image scanners, the image information of a document surface is read photoelectrically while a read optical system scans the document surface placed on an original placement glass. In such apparatuses, running bodies (carriages) having an optical system of a light source (a lamp) and mirrors for transmitting the image information of the document surface to a photoelectric conversion part including a charge-coupled device (CCD) are moved linearly so that the entire document surface is optically scanned and read.
Normally, a stepper motor is used to move the running bodies. The rotation of the stepper motor is transmitted to a drive shaft through a timing belt and a pulley so that a driving force is transmitted to the running bodies by a wire wound around a wire (drive) pulley attached to the drive shaft. By this mechanism, the running bodies are slid along guide rails.
In the case of performing such scanning and reading, the running bodies (or the read optical system provided therein, whose position is adjusted with respect to the running bodies) driven by the wire are required to be maintained in a constant state so as to move in a direction to cross an original sheet at a right angle. However, this requirement is not satisfied by a mere assembly of components since the drive wire, optical system components, and component housings may include size variations, making it difficult to obtain the required right angle. Particularly, in the case of moving the running bodies with a plurality of drive wires, in order to keep the moving direction of the optical part (running bodies) at a right angle to the original sheet, it is necessary to adjust the assembly positions of the running bodies and a drive mechanism including the drive wires relative to each other so that driving forces exerted on the running bodies through the multiple wires are balanced when the running bodies are set in correct positions to move in the direction to cross the original sheet at a right angle.
Conventionally, in the case of employing a drive mechanism transmitting a driving force by winding wires around a plurality of pulleys attached to a single drive shaft, this adjustment has been made by adjusting the attachment positions of the pulleys, which are detachably attached to the drive shaft by fixing screws. After thus adjusting a relationship between the assembly positions of the running bodies and the drive mechanism, the pulleys are fixed to adjusted positions on the drive shaft with-the fixing screws. Specifically, a screw hole is formed in each of the drive pulleys around which the drive wires are wound, and a hexagon head bolt is screwed into each screw hole and tightened with its end part being pressed onto the drive shaft, thereby fixing the pulleys to the drive shaft.
The procedure to be followed at the time of the adjustment is as follows. First, with the drive pulleys being unfixed to the drive shaft with the hexagon head bolts being loose, the running bodies (carriages) are fixed with positioning pins to positioning reference holes provided in guide rails for fixing the running bodies to proper positions. When the running bodies are fixed, the wires connected to the running bodies, the drive pulleys around which the wires are wound, and the drive shaft are properly positioned relative to one another automatically. Then, in the thus determined positions, the drive pulleys are fixed to the drive shaft by tightening the hexagon head bolts.
The conventional drive pulleys employed in drive units as described above are formed of aluminum by die casting. When necessary, cutting is performed as secondary processing for further accuracy. However, this processing method includes a large number of processing steps, thus causing the problems of high production cost and increased weight of each drive pulley.
Further, in the case of employing the above-described method, by which the drive pulleys are fixed to the drive shaft by screwing the hexagon head bolts into the screw holes of the drive pulleys and fastening the hexagon head bolts with their end parts being pressed onto the drive shaft, a special tool (a wrench for hexagon head bolts) is required instead of a common screwdriver, thus increasing the number of steps of the assembly process. Further, according to this method, the hexagon head bolts are screwed into the screw holes with their end parts being in direct contact with the drive shaft, thus damaging the drive shaft. Therefore, when readjustment is carried out and the hexagon head bolts are again tightened after replacement or repairing of components, the hexagon head bolts follow previously damaged positions. This may cause slight deviations of the positions of the drive pulleys on the drive shaft. These deviations of the positions cause deviations of positions of the running bodies, and further, a deviation of the optical axis of the read optical system provided in the running bodies, thus deteriorating the data of a read image.
In a drive mechanism employing these drive pulleys, a reduction in the accuracy of a pulley diameter and the accuracy of run-out from the drive shaft due to the misalignment of the drive shaft and the pulleys deteriorates an error in the moving speed of each running body. Therefore, an error in the outside diameter of each pulley and the run-out thereof should be minimized, thus requiring higher accuracy in the size of each component. In addition, since the screw holes into which the hexagon head bolts are screwed are required to be formed in the pulleys, cutting is further performed on metal castings of little size error for securing accuracy according to the above-described conventional method employing the hexagon head bolts. Thus, higher costs have been required for finishing the drive pulleys with good accuracy.